The present invention relates generally to fluxing practices that remove impurities from molten aluminum, and particularly to the use of at least two mechanical stirrers and the addition of fluxing gas introduced into the molten aluminum beneath each of the mechanical stirrers.
U.S. Pat. No. 5,342,429 to Ho Yu et al, which issued Aug. 30, 1994, discusses the problems with impurities in molten aluminum, such impurities including oxide particles, dissolved gas and chemical impurities such as calcium, sodium, magnesium and lithium. The disclosure of this patent is fully incorporated herein by reference. Mr. Yu is one of the inventors of the present disclosure and application.
Standard processes for fluxing molten aluminum generally employ fluxing gas rates of 0.005 to 0.05 SCFH (standard cubic feet per hour) per pound of metal using a single impeller having a twelve-inch diameter, such as shown in U.S. Pat. No. 3,839,019 to Bruno et al. The rate of rotation of the impeller is at a relatively low rpm, i.e., about 200 rpm. In the case of the above incorporated Yu et al patent, purging gas is introduced into a body of molten aluminum on the order of 0.005 SCFH per pound of aluminum beneath the lowermost of two rotors mounted on a single shaft.